Sucker Rod Coupling and Method of Wear Prevention in Driven Rotation of a Sucker Rod String in Production Tubing

ABSTRACT

A sucker rod coupling features a coupler unit having internally threaded coupling sections at opposite ends for engaging sucker rod pins and one or two outer members extending about the coupler unit between the ends, each outer member being rotatable about the coupler unit and presenting contact surfaces facing outwardly at positions radially outward therefrom. Each outer member is positioned between a respective end of the coupler and a stop defining feature thereof, and a respective stop element is selectively deployable adjacent the respective end of the coupler on a side of the outer member opposite the stop-defining feature. The outer member prevents wear to the production tubing and the sucker rod string, is easily replaceable through manipulation of the stop element to allow sliding of the member off the unit and sliding of a new member thereon, and directly engages the sucker rods without needing additional threaded components.

FIELD OF THE INVENTION

The present invention relates generally to a coupling arrangement forinterconnecting adjacent sucker rods in a string of sucker rods andpreventing wear of production tubing under driven rotation of the suckerrod string within a well bore.

BACKGROUND OF THE INVENTION

In pumping of fluids from a wellbore for production to the surface, astring of sucker rods connected end to end is used as a mechanical linkbetween drive equipment at the surface and a downhole pump in thewellbore for driven operation thereof. Sucker rods are each externallythreaded at pin ends of the rod and are conventionally interconnected byinternally threaded box couplings each threadingly receiving ends ofadjacent rods in the string. The present application is particularlyconcerned with wells using rotationally driven downhole pumps, where thesucker rod string is rotated to provide the rotational, not reciprocal,input required to operate this type of pump. A common problem in suchinstallations is that the sucker rod string does not extend entirelylinearly in the wellbore, and accordingly box couplings between therods, which are of larger outer diameter than the rods themselves andthus form the radially outermost extents of the string, will tend tobump or rub against the production tubing wall during the drivenrotation of the rod string and thus cause significant wear to theproduction tubing. Accordingly, some solutions for preventing orlimiting this wearing of the production tubing have been previouslyproposed to avoid the need for costly repair or replacement of damagedtubing.

One prior art solution has been to bond elastomeric materials to thehard outer surfaces of sucker rod couplers to reduce wear to the tubing,which is more difficult and costly to replace than a coupler. However,the coating may quickly wear away, requiring frequent replacement orrecoating of sucker rod couplers.

U.S. Pat. No. 4,757,861 and 4,919,202 each teach a cylindricalshaft-like body that has a vaned cylindrical wheel of elastomericmaterial disposed and freely rotatable thereabout. The ends of the bodyare externally threaded in order to each engage a box coupling receivinga sucker rod therein from the opposite end thereof. The wheel is ofgreater outer diameter than the box couplers and accordingly forms theonly contact between the rod string and the production tubing or wellcasing, and due to the relative rotation allowed between the wheel andthe central body, moves very slowly, if at all, under the drivenrotation of the rod string. This lack of significant rotation and theuse of elastomeric material minimizes wear to the production tubing orwell casing.

However, these two prior art solutions each rely on a three-pieceassembly to achieve both the wear prevention and rod coupling functions.In other words, the wear prevention structure needs is installed betweenadjacent sucker rods using a pair of box couplings. Installation thusrequires threading of a box coupling on a sucker rod above the wearpreventing structure, threading of the cylindrical body of the wearprevention structure to that box coupling, threading of a second boxcoupling onto the opposite end of the cylindrical body, and threading ofthe second box coupling onto the next sucker rod. It would be desirableto provide a sucker rod coupling and wear prevention arrangement that iseasier to install in a sucker rod string.

In view of the forgoing and other shortcomings of the prior art, thereis a desire for improvement in coupling of sucker rods and wearprevention in driven rotation of sucker rod strings in wellbores.

SUMMARY OF THE INVENTION

According to a first aspect of the invention there is provided a suckerrod coupling comprising:

a coupler unit defined by a unitary body structure having a centrallongitudinal axis passing therethrough and comprising first and secondcoupling sections defining opposite first and second ends of the couplerunit, each coupling section having internal box threading for selectivethreaded engagement with a respective sucker rod at an externallythreaded pin end thereof; and

one or two outer members extending about the coupler unit between thefirst and second ends thereof, each outer member being rotatable aboutthe central longitudinal axis relative to the coupler unit andpresenting contact surfaces facing outwardly away from the coupler unitat positions radially outward therefrom relative to the centrallongitudinal axis;

each outer member being disposed between a respective one of the firstand second ends of the coupler unit and a respective stop-definingfeature of the unitary body that projects radially outward further fromthe longitudinal axis than a portion of the coupler unit around whichthe outer member extends without reaching past the contact surfaces ofthe outer member so as to block sliding of the outer member past thestop-defining feature along the longitudinal axis; and

a respective stop element corresponding to each outer member and beingselectively deployable adjacent the respective one of the first andsecond ends of the coupler unit on a side of the outer member oppositethe stop-defining feature to project radially outward from an outersurfaces of the coupling section without reaching past the contactsurfaces of the outer member so as to block sliding of the outer memberpast the deployed stop element, the outer member being slidable off therespective end of the coupler unit when the stop element is notdeployed.

Preferably each outer member extends around the coupler unit at arespective one of the coupling sections at a position past which theinternal box threading reaches along the longitudinal axis away from therespective end of the coupler unit.

Preferably each respective stop element comprises a ring releasablyengagable around the coupler body adjacent the respective end of thecoupler unit.

Preferably each ring is a snap ring engagable into a respective groovein the outer surface of the coupling section defining the respective endof the coupler unit.

The internal box threading of both coupling sections may be disposedwithin a common internal passage extending fully through the couplerunit along the longitudinal axis. A single internal thread in the commoninternal passage may define the box threading of both coupling sections.Is this right?

Each outer member may be defined by an outer race of a bearing assembly,the outer face closing fully about the coupler. Each bearing assemblymay further comprise an inner race closing about the coupler, wherebythe inner and outer races and roller elements therebetween are movabletogether along the longitudinal axis for selective removal of thebearing assembly from the coupler.

In use, the sucker rod coupling is coupled between adjacent sucker rodsin a sucker rod string to form a section thereof, the adjacent suckerrods comprising upper and lower rods engaged to upper and lower ones ofthe coupling sections of the coupling unit and the sucker rod stringbeing driven for rotation within production tubing in a wellbore,whereby contact of the contact surfaces of the outer member of thesucker rod coupling with an inner wall surface of the production tubingunder driven rotation of the sucker rod string cooperates with allowedrelative rotation between the outer member and the coupler to avoiddirect contact between the production tubing and the rotating sucker rodstring to prevent or limit wear to either thereof.

In one embodiment, there is only one outer member and only onerespective stop element deployable adjacent a bottom end of the couplerunit, an upper one of the coupling sections having a larger outerdiameter than a lower one of the coupling sections around which theouter member is positioned and a step in diameter between the couplingsections forming the stop-defining feature. Preferably the larger outerdiameter of the upper coupling section of the coupler unit is equal toan outer diameter of a portion of the respective sucker rod to which thecoupler unit is to be coupled. Preferably the larger diameter of theupper coupling section of the coupler unit is equal to the outerdiameter of a pin connection shoulder of the respective sucker rod.

In another embodiment, the at least one outer member comprises separatefirst and second outer members spaced apart along the longitudinal axisand disposed adjacent the first and second ends of the coupler unitrespectively. The coupler with two outer members preferably comprises awrench engagable section defined between the first and second couplingsections, and the wrench engagable section preferably comprises opposingplanar surfaces on opposite sides of the longitudinal axis.

According to a second aspect of the invention there is provided a methodof operating and retrieving a sucker rod string within production tubingin a well bore, the method comprising:

providing a sucker rod coupling that is in accordance with the firstaspect of the invention and has only one outer member and only onerespective stop element deployable adjacent a bottom end of the couplerunit, an upper one of the coupling sections having a larger outerdiameter than a lower one of the coupling sections around which theouter member is positioned and a step in diameter between the couplingsections forming the stop-defining feature, and the larger outerdiameter of the upper coupling section of the coupler unit being equalto an outer diameter of a portion of the respective sucker rod to whichthe coupler unit is to be coupled;

installing the sucker rod coupling between the respective sucker rods byengaging the first and second coupling sections of the coupler unit tothe respective sucker rods to form part of the sucker rod string fromthe coupler unit and the respective sucker rods engaged therewith;

driving rotation of the sucker rod string within the production tubing;

during driven rotation of the sucker rod string, using contact betweenthe contact surfaces of each outer member of the sucker rod coupling andan inner wall surface of the production tubing to prevent contact of theproduction tubing with the rotating sucker rods and the coupler unitrotating therewith; and

after failure of the part of the sucker rod string at an upper one ofthe respective sucker rods between which the sucker rod coupling isinstalled, retrieving the sucker rod coupling and sucker rods therebelowby using the upper coupling section thereof of the coupling unit as afish neck to grip the upper coupling section with a fishing tooldimensionally compatible with a sucker rod size of the sucker rodstring.

According to a third aspect of the invention there is provided a suckerrod coupling comprising:

a coupler unit extending having a central longitudinal axis passingtherethrough and comprising first and second coupling sections definingopposite first and second ends of the coupler unit, each couplingsection being configured for selective attachment to a respective suckerrod; and

at least one outer member extending about the coupler unit between thefirst and second ends thereof, each outer member being rotatable aboutthe central longitudinal axis relative to the coupler unit andpresenting contact surfaces facing outwardly away from the coupler unitat positions radially outward therefrom relative to the centrallongitudinal axis.

The at least one outer member may comprise first and second outermembers spaced apart along the longitudinal axis and disposed adjacentthe first and second ends of the coupler unit respectively, in whichcase first and second internal passages may extend into the first andsecond coupling sections from the first and second ends of the couplerunit respectively to engagingly receive ends of the respective suckerrods, the first and second outer members extending about the couplerunit at positions along the first and second internal passagesrespectively,

Preferably each internal passage is threaded for selective threadedengagement with a matingly threaded end of the respective sucker rod.

Preferably there are provided stops defined at ends of the first andsecond coupling sections opposite the first and second ends of thecoupler unit and projecting radially outward from outer surfaces of thecoupling sections where the outer members extend thereabout to limitsliding of the outer members toward one another along the longitudinalaxis.

Preferably there are provided stop elements selectively deployable atpositions between the first and second outer members and the first andsecond ends of the coupler unit to project radially outward from theouter surfaces of the coupling sections where the outer members extendthereabout to limit sliding of the outer members away from one another,the outer members being slidable off the ends of the coupler unit whenthe stop elements are not deployed.

According to a fourth aspect of the invention there is provided a methodfor preventing wear under driven rotation of a sucker rod string withinproduction tubing in a well bore, the method comprising:

providing a sucker rod coupling comprising a coupler unit extendingalong a central longitudinal axis passing therethrough and comprisingfirst and second coupling sections defining opposite first and secondends of the coupler unit, each coupling section being configured forselective attachment to a respective sucker rod; and at least one outermember extending about the coupler unit between the first and secondends thereof, each outer member being rotatable about the centrallongitudinal axis relative to the coupler unit and presenting contactsurfaces facing outwardly away from the coupler unit at positionsradially outward therefrom relative to the central longitudinal axis;

installing the sucker rod coupling between the respective sucker rods byengaging the first and second coupling sections of the coupler unit tothe respective sucker rods to form part of the sucker rod string fromthe coupler unit and the respective sucker rods engaged therewith; and

driving rotation of the sucker rod string within the production tubing;

during driven rotation of the sucker rod string, using contact betweenthe contact surfaces of each outer member of the sucker rod coupling andan inner wall surface of the production tubing to prevent contact of theproduction tubing with the rotating sucker rods and the coupler unitrotating therewith.

Preferably the sucker rod coupling comprises a wrench engagable sectiondefined between the first and second coupling sections at a positionspaced from each outer member along the longitudinal axis and eachcoupling section of the coupler unit is threaded for engagement with amatingly threaded end of the respective sucker rod, the methodcomprising using a wrench to rotate the coupler unit about thelongitudinal axis at the wrench engagable section to loosen or tightenthreaded connection of the coupler unit within the rod string.

The wrench engagable section of the coupler unit may comprise opposingplanar surfaces on opposite sides of the longitudinal axis.Alternatively, the wrench-engagable section may be circular incross-section and engagable by a pipe wrench to effect rotation of thecoupler unit.

BRIEF DESCRIPTION OF THE DRAWINGS

In the accompanying drawings, which illustrate exemplary embodiments ofthe present invention:

FIG. 1 is a side elevational view of a central body of a sucker rodcoupling according to a first embodiment of the present invention.

FIG. 2 is an overhead plan view of the central body of the sucker rodcoupling of FIG. 1.

FIG. 3 is a schematic illustration of the sucker rod coupling of FIG. 1in use within a wellbore to couple together sucker rods in a string andprevent wear to the production tubing in which the sucker rods are used.

FIG. 4 is a perspective view of the central body of the sucker rodcoupling of FIG. 1.

FIG. 5 is a perspective view of a sucker rod coupling according to asecond embodiment of the present invention.

FIG. 6 is an exploded side elevational view of the sucker rod couplingof FIG. 5.

FIG. 7 is a schematic illustration of the sucker rod coupling of FIG. 5in use within a wellbore to couple together sucker rods in a string andprevent wear to the production tubing in which the sucker rods are used.

DETAILED DESCRIPTION

FIG. 1 shows a central coupler unit 10 of a sucker rod coupling of afirst embodiment of the present invention. The coupler unit 10 isdefined by a single integral unitary body of solid material having anelongated shape oriented to lie lengthwise on a longitudinal axis 12passing centrally therethrough. Along its length, the body 10 features afirst coupling section 14 defining a planar first end 16 of the body, asecond coupling section 18 defining an opposite planar second end 20 ofthe body and a middle wrench section 22 interconnecting the couplingsections along the longitudinal axis 12. Each coupling section 14, 18features a cylindrical portion of the body that has been hollowed byformation of a bore 24 extending into the body from the respectiveplanar end face of the body defined by that cylindrical portion in orderto form an internal passage in the coupling section into which the endof a sucker rod can be inserted. The bore 24 has a circular crosssection concentric with the circular cross section of the cylindricalportion into which it extends and, as shown in the partially sectionedillustration of FIG. 3, is threaded according to the thread pattern ofan externally threaded male or pin end 26 a of a conventional sucker rod26 to facilitate threaded engagement of the sucker rod end 26 a into theinternally threaded female or box end section of the coupler body 10.

At a distance along the longitudinal axis 12 from each end face 16, 20of the coupler body 10, the outer diameter of the coupling section 14,18 increases by a single step to form a larger cylindrical portion 28concentric and end-to-end with the smaller cylindrical portion 30defining the respective end face 16, 20 of the coupler body 10. Ashoulder formed at this change in diameter of each coupling section 14,18 defines a ledge in the form of an annular stop face or surface 32projecting radially outward from the smaller diameter portion 30 of thecoupling section in a plane normal to the longitudinal axis 12. Acircumferential groove 34 in the outer peripheral surface of the smallerdiameter portion 30 of each coupling section 14, 18 extends fullytherearound about the longitudinal axis at a location therealong a shortdistance inward from the respective end face 16, 20 of the coupler body10.

With reference to FIG. 3, the final structure of the sucker rod couplingof the first illustrated embodiment is completed by installation of abearing 36 and snap ring 37 on each coupler section 14, 18 of thecoupler body 10. Each bearing 36 is of a conventional structure havingan inner race member 38, an outer race member 40 and a plurality ofrolling elements 42 disposed therebetween. Each bearing 36 is disposedabout the smaller diameter portion 30 of the respective coupler section14, 18 so that the annular or hollow cylindrical inner race member 38 isfrictionally engaged with the outer peripheral surface of the couplingsection at this small diameter portion thereof, and the annular orhollow cylindrical outer race member 40 is accordingly rotatablerelative to the fixed-together inner race member and coupler body 10about the longitudinal axis 12 due to the roller elements 42 between theraces. The first illustrated embodiment features needle bearings havingelongated cylindrical roller elements, but it will be appreciated thatother known rolling element bearing types may alternatively be used toallow relative rotation between the outer race member and the couplerbody 10. Furthermore, other embodiments may lack an inner race memberengaged to the coupler body 10, and instead may have roller elementsdisposed directly between an outer race member and the coupler body 10,relying on outer surfaces of the coupler body to define the inner raceof the bearing assembly.

The larger diameter portion 28 of each coupler section 14, 18 of thecoupler body 10 locates the respective bearing 36 along the longitudinalaxis 12 under sliding of the bearing 36 onto the coupler body 10 fromthe respective end 16, 20 thereof during assembly of the sucker rodcoupling, this large diameter portion 28 acting as a stop to limitmovement of the bearings toward each other and toward the middle wrenchportion 22 of the coupler body 10 when the end face of the bearingreaches the ledge or stop surface 32 at the juncture of the small andlarge diameter portions of the respective coupling section of thecoupler body 10. The snap ring of each coupling sections 14, 18 is thenengaged into the groove 34 on the side of the respective bearing 36opposite the large diameter stop-defining portion 28 of the couplingsection 14, 18 to complete the positioning of the bearing 36 along thelongitudinal axis 12 by blocking movement of the bearing 36 away fromthe middle section and the opposite bearing to the respective end 16, 20of the coupler body 10. The snap rings 37 thus provide removable stopelements that can be installed and removed as needed to allow forpossible removable of the bearings 36 if required, the installation ofthe snap ring 37 forming a stop deployed on the coupler body 10 toproject radially outward from the outer peripheral surface of thesmaller diameter portion 30 of the respective coupling section 14, 18 toblock sliding movement of the installed bearing 36 past it along thelongitudinal axis. It will be appreciated that other selectivelydeployable stop elements may be used in place of snap rings to positionthe bearings when deployed and allow removal of the bearings when notdeployed. For example, the end of the coupling body could be externallythreaded for engagement with an internally threaded nut or stop ring toallow installation and removal of the nut on the side of the bearingopposite the fixed or permanent larger diameter stop-defining portion 28of the respective coupling section. However, the snap ring has theadvantage that it will maintain it position along the longitudinal axisregardless of any inadvertent rotation thereof since the axial positionof the snap ring is locked by its positive positioning within thegroove. Also, use of an internally threaded nut or stop would requirethat such piece be sufficiently small so as not to project further fromthe coupling unit that the bearing to ensure that only the bearingcontacts the production tubing surrounding the coupling.

FIG. 3 shows the sucker rod coupling in use within the bore 100 of awell. The threaded internal passage 24 of the first coupling section 14has been engaged with the externally threaded pin end 26 a at the bottomof a sucker rod 26 disposed above the coupling in the well bore 100, andthe threaded internal passage of the second coupling section 18 haslikewise been engaged with the externally threaded pin end at the top ofa sucker rod disposed below the coupling in the well bore 100 so thatthe coupling body 10 acts to couple the two sucker rods together andaccordingly forms part of the overall sucker rod string that is drivenfor rotation to operate a downhole pump. The bearings 36 of the couplingextend outwardly beyond any and all portions of the coupler body 10 inradial planes normal to the longitudinal axis 12 thereof. The outerperipheral surfaces of the outer race members of the bearings 36 facingoutwardly away from the coupler body relative to the longitudinal axis12 accordingly define the radially outermost extents of the coupling,and therefore define cylindrical contact surfaces that will contact thesurrounding cylindrical inner wall surface of the production tubing 102before any portion of the two sucker rods and the coupler bodytherebetween is allowed to reach the production tubing 102 undermovement of this rod string portion out of alignment with a central axisof the section of the production tubing string 102. With frictionalcontact between the outer race of one of the bearings and thesurrounding tubing wall 102 closing thereabout, the outer race isstationary with respect to rotation about the longitudinal axis whilethe inner race, and the coupler body 10 on which it is fixed, arerotated about the longitudinal axis 12 by the driven rotation of thesucker rods. Accordingly, there is no relative movement between thebearing contact surfaces that make contact with the production tubing,and so wear of the tubing that would otherwise occur under contact ofany part of the spinning rod string with the production tubing isavoided. If the outer race of the bearing does rotate somewhat under thedriven rotation of the string, it will be at significantly reduced speedcompared to that of the string, and so the degree of wear is stillreduced from what would occur without use of the coupling.

In the first illustrated embodiment, the middle wrench section 22 of thecoupler body 10 is concentric with the coupling sections and is squarein cross-section with a corner-to-corner diameter less than the circulardiameter of both the small and large diameter portions of the equallydimensioned coupling sections. This square wrench section provided twopairs 22 a, 22 b of parallel, planar opposing faces across thelongitudinal axis 12, each pair of opposing faces thus defining wrenchflats by which the wrench section can be engaged by opposing jaws of awrench in order to rotate the coupler body 10 about its central axis 12to effect tightening and loosening in threaded coupling and decouplingof the coupler body 10 with a sucker rod. It will be appreciated thatother non-square cross-sections may be used in the wrench section of thecoupling body while still presenting at least one pair of opposingplanar surfaces or wrench flats. Alternatively, a circular or othercurved peripheral shape may be used in the cross-section of the middlepart of the coupler body, and still be engagable by a pipe wrench toeffect rotation of the coupler body relative to a sucker rod in couplingor decoupling therefrom.

The coupler body is preferably a single integral unitary body of steel,for example 4140 HTSR steel machined to shape the different sections,but those of skill in the art will recognize alternate materials andproduction methods that may be used to form the coupler body having thedifferent sections described. For example, a coupler body formed bymultiple pieces rigidly fixed together during production of the couplingcould similarly form a one-piece coupler unit for direct connectionbetween sucker rods without additional coupling pieces separate from thecoupler unit. Timken B-2420 and B-2824 are examples of bearings that maybe used, and suitable dimensioning of stops and bearing-carryingportions of the coupler body for cooperation with such bearings iswithin the ambit of those skilled in the art. These differently sizedexemplary bearings having different outer diameters illustrate howsucker rod couplings of the present invention may be produced indifferent sizes to better fit differently sized production tubing. Thesize of the bearing is selected to have an outer diameter less than theinner diameter of the production tubing, thereby leaving space betweenthe bearing and the tubing wall through which the fluid being producedby operation of the downhole pump can pass, even when part of thebearing's outer surface is in contact with the tubing wall. Otherbearings may be used, or sleeves or wheels of metal, plastic or othermaterials may be fitted about the coupler body using an interface otherthan rollers elements but of low enough friction between the sleeve andbody to allow relative rotational motion therebetween about thelongitudinal axis. The use of any such rotatable outer member disposedabout a central body that not only forms the spinning core or shaftcarrying the outer member but also forms coupling sections for directconnection to sucker rods without requiring separate additional couplersbetween the body and the sucker rods presents advantage over prior artarrangements requiring fastening together of multiple separate pieces toachieve both a wear preventing function and coupling of adjacent suckerrods.

Accordingly, embodiments using only one outer member rotatable relativeto the central coupling body would still provide such advantage over theprior art, just as embodiments lacking a specific section for engagementby a wrench would share this advantage. The first illustrated embodimentprovides further benefit by using two outer members at spaced positionsalong the central body to better resist deviation of the body's axissufficiently out of line with the well bore axis to, and even furtherbenefit by providing a central wrench engagable portion disposedbetween, and thus left uncovered and unobstructed by, the two outermembers.

FIGS. 5 and 6 show a second embodiment sucker rod coupler that uses asingle plastic sleeve to provide the contact area of the coupler withthe production tubing instead of the two bearings of the firstembodiment.

Carrying only a single sleeve, the coupler unit of this embodiment issignificantly smaller than that of the first embodiment and has asimpler overall structure, meaning that the coupler may be produced at alower cost and marketed as a more cost efficient option than the firstembodiment.

With reference to the exploded view of the coupling in FIG. 6, thecoupler unit 10′ of the second embodiment is again defined by a singleintegral unitary body of rigid material having an elongated shapeoriented to lie lengthwise on a longitudinal axis 12′ passing centrallytherethrough. Along its length, the body 10′ features a first couplingsection 14′ defining a planar first end 16′ of the body and a secondcoupling section 18′ defining an opposite planar second end 20′ of thebody. The second embodiment lacks the wrench section of the firstembodiment. Each coupling section 14′, 18′ features a respectivecylindrical portion of the body that has been hollowed by formation of asingle bore 24′ extending fully through the body from the on planar endface thereof to the other to form a single internal passage into eachend of which the pin end of a sucker rod can be received. The bore 24′has a circular cross section concentric with the circular cross sectionof the cylindrical body portions through which it passes and, as shownin broken lines in FIG. 6, is threaded according to the thread patternof an externally threaded male or pin end of a conventional sucker rodto facilitate threaded engagement of the pin ends of two sucker rodsinto the threaded internal passage from opposite ends of the couplerbody 10′.

Still referring to FIG. 6, at a distance along the longitudinal axis 12′from each end face 16′, 20′ of the coupler body 10′, the outer diameterof the coupling section 14, 18 features a single step change, decreasingfrom the upper first coupling section 14′ to the lower second couplingsection 18′. A shoulder formed at this change in diameter of between thetwo coupling sections 14′, 18′ defines a ledge in the form of an annularstop face or surface 32′ projecting radially outward from the smallerdiameter lower coupling section 18′ in a plane normal to thelongitudinal axis 12′. A circumferential groove 34′ in the outerperipheral surface of the smaller diameter lower coupling section 18′extends fully therearound about the longitudinal axis at a locationtherealong a short distance inward from the bottom end face 20′ of thecoupler body 10′.

With reference to FIG. 5, the final structure of the sucker rod couplingof the second illustrated embodiment is completed by installation of asleeve 36′ and snap ring 37′ on the lower coupler section 18′ of thecoupler body 10′. The plastic sleeve 36′ has a cylindrical outer surfaceclosing around the longitudinal axis 12′ and a cylindrical inner borecentered thereon. The sleeve 36′ is disposed about the smaller diameterlower coupling section 18′ with the bore diameter of the sleeve 36′slightly exceeding the outer diameter of the lower coupling section 18′so that the sleeve 36′ is accordingly rotatable relative to the couplerbody 10′ about the longitudinal axis 12′.

The larger diameter upper coupler section 14′ of the coupler body 10′locates the sleeve 36′ along the longitudinal axis 12′ under sliding ofthe sleeve 36′ onto the coupler body 10′ from the bottom end 20′ thereofduring assembly of the sucker rod coupling, this large diameter couplingsection 14′ acting as a stop to limit movement of the sleeve toward thetop end 16′ of the coupler body 10′ when the end face of the bearingreaches the ledge or stop surface 32′ at the juncture between thecoupling sections 14′, 18′. The snap ring 37′ is then engaged into thegroove 34′ on the side of the sleeve 36′ opposite the large diameterstop-defining upper coupling section 14′ to complete the positioning ofthe sleeve 36′ along the longitudinal axis 12′ by blocking movement ofthe sleeve 36′ away from the upper coupling section 14′ to the bottomend 20′ of the coupler body 10. The snap ring 37′ thus provides aremovable stop element that can be installed and removed as needed toallow for possible removable of the sleeve 36′ by sliding off the bottomend of the coupling unit if required, the installation of the snap ring37′ forming a stop deployed on the coupler body 10 to project radiallyoutward from the outer peripheral surface of the smaller diameter lowercoupling section 18′ to block sliding movement of the installed sleeve36′ past it along the longitudinal axis.

FIG. 7 shows the sucker rod coupling in use within the bore of a well.The threaded internal passage 24′ of the coupling unit 10′ has beenengaged at its top end with the externally threaded pin end 126 a at thebottom of a sucker rod 126 disposed above the coupling in the well bore100, and at its bottom end with the externally threaded pin end at thetop of a sucker rod disposed below the coupling in the well bore 100 sothat the coupling body 10 acts to couple the two sucker rods togetherand accordingly forms part of the overall sucker rod string that isdriven for rotation to operate a downhole pump. The sleeve 36′ of thecoupling extends outwardly beyond any and all portions of the couplerbody 10′ in radial planes normal to the longitudinal axis 12′ thereof.The outer peripheral surfaces of the outer sleeve 36′ facing outwardlyaway from the coupler body relative to the longitudinal axis 12′accordingly define the radially outermost extents of the coupling, andtherefore define cylindrical contact surfaces that will contact thesurrounding cylindrical inner wall surface of the production tubing 102before any portion of the two sucker rods and the coupler bodytherebetween is allowed to reach the production tubing 102 undermovement of this rod string portion out of alignment with a central axisof the section of the production tubing string 102. With frictionalcontact between the sleeve and the surrounding tubing wall 102 closingthereabout, the sleeve is stationary with respect to rotation about thelongitudinal axis while the coupler body 10′ is rotated about thelongitudinal axis 12′ by the driven rotation of the sucker rods.Accordingly, there is no relative movement between the sleeve contactsurfaces that make contact with the production tubing, and so wear ofthe tubing that would otherwise occur under contact of any part of thespinning rod string with the production tubing is avoided. If the sleevedoes rotate somewhat under the driven rotation of the string, it will beat significantly reduced speed compared to that of the string, and sothe degree of wear is still reduced from what would occur without use ofthe coupling.

The second embodiment coupler thus operates similar to the firstembodiment and shares the same advantage of direct coupling to thesucker rods it connects in order to avoid use of box connection piecesseparate from the single body piece around which the outer member(whether a bearing or sleeve) rotates. The two illustrated embodimentsalso share the advantage that each such outer member is selectivelyremovable from the coupler unit for replacement, by disengagement of thesnap ring from the groove adjacent the end of the coupler unit to allowsliding of the outer member off that end of the unit. Both embodimentsmake use of the lower coupling section to not only provide the threadedcoupling to the respective sucker rod, but also to provide a bearing orsleeve carrying portion of the coupler, with the first embodimentlikewise having such dual functionality of the upper coupling section.This dual functionality provides material savings in reducing that sizeof the overall coupler, thus saving on production cost.

With reference to FIG. 7, the second embodiment provides furtheradvantage by having the outer diameter of the upper coupling section 14′equal to the outer diameter of the pin shoulder 126 b of the sucker rods126 in the string. This way, should there be a failure at the pinconnection 126 a of the sucker rod 126 above the coupler to the couplerunit 10′, a conventional overshot fishing tool suitably dimensioned forcompatibility in drawing out the size of sucker rod used in the stringby its pin shoulder 126 b can be used to fish out the coupler and thesucker rods connected below it by gripping the coupler unit 10′ at theouter peripheral surface of its upper coupling section 14′. This way, nonew, different or specialized fishing tool is required to retrieve theremaining rod string portion stuck in the wellbore, as an existingsucker-rod fishing tool configured for the known sucker rod size can beemployed in the conventional manner to grip the upper coupling section14′ of the sucker rod coupler in the same manner as it would typicallybe used to grip the pin shoulder of one of the sucker rods. As shown inFIG. 7, the overall length of the coupler unit only slightly exceeds thecombined length of the pins of the two sucker rods connected by it,which combines with the dual functionality of the lower coupling section18′ to make efficient use of material in the smaller resulting coupling.The lower coupling section 18′ is just long enough to fit the axiallength of the sleeve 36′ between the groove positioned at the bottom endof the coupler unit and the shoulder-like stop defined the joint of thetwo coupling sections 14′, 18′.

A prototype of the second embodiment coupler uses a roller-like piece ofvirgin ultra high molecular weight polyethylene (RecoTM UHMW-PE naturalvirgin from Redwood Plastics Corporation) to provide a sleeve having ahigh impact strength, high chemical and wear/abrasion resistance and lowcoefficient of friction, but it will be appreciated that sleeves ofother materials may alternatively be employed. Likewise, although theillustrated sleeve 36′ features a continuously curved cylindrical outersurface, it will be appreciated that other sleeve shapes of non-circularcross section may be similarly employed to provide tubing contactsurfaces radially outward from the rest of the coupler. For example,U.S. Pat. Nos. 4,757,861 and 4,919,202 show how a vaned wheel ofelastomeric material or fluted and/or notched tubular sleeve of softresilient abrasion resistant material may be used to contact the welltubing around a sucker rod string while providing significant open areasin the wheel or sleeve's cross section to ensure that fluid can flowpast it. Such material and shape configurations may similarly beemployed in the present invention in place of the illustrated secondembodiment sleeve of substantially cylindrical shape (purely cylinderouter surface, except at short tapered end portions of the sleeve) orillustrated first embodiment bearing(s).

Since various modifications can be made in my invention as herein abovedescribed, and many apparently widely different embodiments of same madewithin the spirit and scope of the claims without department from suchspirit and scope, it is intended that all matter contained in theaccompanying specification shall be interpreted as illustrative only andnot in a limiting sense.

1. A sucker rod coupling comprising: a coupler unit defined by a unitarybody structure having a central longitudinal axis passing therethroughand comprising first and second coupling sections defining oppositefirst and second ends of the coupler unit, each coupling section havinginternal box threading for selective threaded engagement with arespective sucker rod at an externally threaded pin end thereof; and atleast one outer member extending about the coupler unit between thefirst and second ends thereof, each outer member being rotatable aboutthe central longitudinal axis relative to the coupler unit andpresenting contact surfaces facing outwardly away from the coupler unitat positions radially outward therefrom relative to the centrallongitudinal axis; each outer member being disposed between a respectiveone of the first and second ends of the coupler unit and a respectivestop-defining feature of on the unitary body that projects radiallyoutward further from the longitudinal axis than a portion of the couplerunit around which the outer member extends without reaching past thecontact surfaces of the outer member so as to block sliding of the outermember past the stop-defining feature along the longitudinal axis; and arespective stop element corresponding to each outer adjacent therespective one of the first and second ends of the coupler unit on aside of the outer member opposite the stop-defining feature to projectradially outward from an outer surfaces of the coupling section withoutreaching past the contact surfaces of the outer member so as to blocksliding of the outer member past the stop element.
 2. (canceled)
 3. Thesucker rod coupling according to claim 1 wherein each respective stopelement comprises a ring releasably engagable around the coupler bodyadjacent the respective end of the coupler unit.
 4. The sucker rodcoupling according to claim 3 wherein each ring is a snap ring engagableinto a respective groove in the outer surface of the coupling sectiondefining the respective end of the coupler unit.
 5. The sucker rodcoupling according to claim 1 wherein an upper one of the couplingsections has a larger outer diameter than the portion of the couplerunit around which the outer member extends, and the stop definingfeature is formed by a step in diameter between the upper couplingsection and the portion of the coupler unit around which the outermember extends.
 6. The sucker rod coupling according to claim 5 whereinthe larger outer diameter of the upper coupling section of the couplerunit is equal to an outer diameter of a portion of the respective suckerrod to which the coupler unit is to be coupled to enable gripping theupper coupling section with a fishing tool dimensionally compatible witha sucker rod size of the sucker rod string.
 7. The sucker rod couplingaccording to claim 6 wherein the larger diameter of the upper couplingsection of the coupler unit is equal to the outer diameter of a pinconnection shoulder of the respective sucker rod.
 8. The sucker rodcoupling according to claim 5 in combination with a sucker rod string,the sucker rod coupling being installed in the sucker rod string betweenadjacent sucker rods, the adjacent sucker rods comprising an upper rodengaged to the upper coupling section and a lower rod engaged to thelower coupling section.
 9. The sucker rod coupling according to claim 1wherein the internal box threading of both coupling sections is disposedwithin a common internal passage extending fully through the couplerunit along the longitudinal axis.
 10. The sucker rod coupling accordingto claim 9 wherein a single internal thread in the common internalpassage defines the box threading of both coupling sections.
 11. Thesucker rod coupling according to claim 1 wherein the at least one outermember comprises separate first and second outer members spaced apartalong the longitudinal axis and disposed adjacent the first and secondends of the coupler unit respectively.
 12. The sucker rod couplingaccording to claim 11 wherein the coupler comprises a wrench engagablesection defined between the first and second coupling sections.
 13. Thesucker rod coupling according to claim 12 wherein the wrench engagablesection comprises opposing planar surfaces on opposite sides of thelongitudinal axis.
 14. The sucker rod coupling according to claim 1wherein each outer member is defined by an outer race of a bearingassembly, the outer face closing fully about the coupler and the bearingassembly further comprising an inner race closing about the coupler androller elements between the inner and outer races.
 15. (canceled) 16.The sucker rod coupling of claim 1 coupled between adjacent sucker rodsin a sucker rod string to form a section thereof, the sucker rod stringbeing driven for rotation within production tubing in a wellbore,whereby contact of the contact surfaces of the outer member of thesucker rod coupling with an inner wall surface of the production tubingunder driven rotation of the sucker rod string cooperates with allowedrelative rotation between the outer member and the coupler to avoiddirect contact between the production tubing and the rotating sucker rodstring to prevent or limit wear to either thereof.
 17. A method ofoperating and retrieving a sucker rod string within production tubing ina well bore, the method comprising: providing a sucker rod couplingcomprising: a coupler unit defined by a unitary body structure having acentral longitudinal axis passing therethrough and comprising upper andlower coupling sections defining opposite upper and lower ends of thecoupler unit, each coupling section having internal box threading forselective threaded engagement with a respective sucker rod at anexternally threaded pin end thereof; and an outer member extending aboutthe coupler unit between the upper and lower ends thereof at a portionof the coupler unit of smaller diameter than the upper coupling section,the outer member being rotatable about the central longitudinal axisrelative to the coupler unit and presenting contact surfaces facingoutwardly away from the coupler unit at positions radially outwardtherefrom relative to the central longitudinal axis; installing thesucker rod coupling between the respective sucker rods by engaging theupper and lower coupling sections of the coupler unit to the respectivesucker rods to form part of the sucker rod string from the coupler unitand the respective sucker rods engaged therewith, the upper couplingsection of the coupler unit being equal in outer diameter to a portionof an upper one of the respective sucker rods to which the uppercoupling section of the coupler unit is engaged; driving rotation of thesucker rod string within the production tubing; during driven rotationof the sucker rod string, using contact between the contact surfaces theouter member of the sucker rod coupling and an inner wall surface of theproduction tubing to prevent contact of the production tubing with therotating sucker rods and the coupler unit rotating therewith; and afterfailure of the part of the sucker rod string at the upper one of therespective sucker rods between which the sucker rod coupling isinstalled, retrieving the sucker rod coupling and sucker rods therebelowby using the upper coupling section of the coupling unit as a fish neckto grip the upper coupling section with a fishing tool dimensionallycompatible with a sucker rod size of the sucker rod string.
 18. Themethod according to claim 17 wherein the outer member of the sucker rodcoupling is disposed between the lower end of the coupler unit and arespective stop-defining feature of the unitary body that projectsradially outward further from the longitudinal axis than the portion ofthe coupler unit around which the outer member extends without reachingpast the contact surfaces of the outer member so as to block sliding ofthe outer member past the stop-defining feature along the longitudinalaxis, and there is provided a respective stop element adjacent the lowerend of the coupler unit on a side of the outer member opposite thestop-defining feature to project radially outward from an outer surfacesof the lower coupling section without reaching past the contact surfacesof the outer member so as to block sliding of the outer member past thetop element.
 19. The method according to claim 17 wherein the uppercoupling section of the coupler unit is equal in outer diameter to a pinconnection shoulder of the upper one of the respective sucker rods. 20.The method according to claim 18 wherein the upper coupling section ofthe coupler unit is equal in outer diameter to a pin connection shoulderof the upper one of the respective sucker rods.
 21. The sucker rodcoupling according to claim 5 wherein there is only one outer member andonly one respective stop element, which is adjacent a bottom end of thecoupler unit.
 22. A sucker rod coupling comprising: a coupler unitdefined by a unitary body structure having a central longitudinal axispassing therethrough and comprising first and second coupling sectionsdefining opposite first and second ends of the coupler unit, eachcoupling section having internal box threading for selective threadedengagement with a respective sucker rod at an externally threaded pinend thereof; and two outer members extending about the coupler unitbetween the first and second ends thereof, each outer member beingrotatable about the central longitudinal axis relative to the couplerunit and presenting contact surfaces facing outwardly away from thecoupler unit at positions radially outward therefrom relative to thecentral longitudinal axis; each outer member being disposed between arespective one of the first and second ends of the coupler unit and arespective stop-defining feature of the unitary body that projectsradially outward further from the longitudinal axis than a portion ofthe coupler unit around which the outer member extends without reachingpast the contact surfaces of the outer member so as to block sliding ofthe outer member past the stop-defining feature along the longitudinalaxis; and a respective stop element corresponding to each outer memberadjacent the respective one of the first and second ends of the couplerunit on a side of the outer member opposite the stop-defining feature toproject radially outward from an outer surfaces of the coupling sectionwithout reaching past the contact surfaces of the outer member so as toblock sliding of the outer member past the stop element; wherein theunitary body of the coupler unit comprises a wrench engagable sectiondefined at a position between the two outer members along the centrallongitudinal axis.